1. Field of the Invention
The present invention relates to an encoding-availability determining apparatus, an encoding-availability determining method, and an encoding-availability determining program that determine whether encoding can be performed to embed data into an image, and more particularly to an encoding-availability determining apparatus, an encoding-availability determining method, and an encoding-availability determining program that enable to determine whether encoding can be performed without actually examining whether data can be extracted from an image by inputting the image from a medium after the image having encoded data is output to the medium.
2. Description of the Related Art
A conventional technology disclosed in U.S. Pat. No. 5,636,292 and Japanese Patent Laid-Open Publication No. 2000-299779 to embed data (code etc.) into image data or sound data is applied to prevent falsification, to prevent fraudulent usage, and to provide additional services. For example, a method to read a digital watermark embedded into a printed material and to display a specified web page is disclosed in U.S. Pat. No. 5,841,978.
An encoding method is disclosed in Japanese Patent Laid-Open Publication No. 2004-349879 in which an image is split into a plurality of blocks, and a difference between average densities of adjacent blocks is used to embed codes into the adjacent block pairs. After the image, which includes the embedded codes, is output to a paper or a display device etc., the image is input by using an input device such as a camera and subjected to a decoding process. In the decoding process, the original codes are decoded from the difference between the average densities of the adjacent blocks of the input image.
In the encoding and decoding method disclosed in Japanese Patent Laid-Open Publication No. 2004-349879, decoding is performed only by using the difference between the average densities of the adjacent blocks of the input image, thereby enabling to enhance the speed of the decoding process. Due to this, a decoder based on the aforementioned decoding method is increasingly mounted on a portable device.
However, in the encoding method disclosed in Japanese Patent Laid-Open Publication No. 2004-349879, color reproduction of the image that is output to a medium such as the paper or the display device is affected due to output characteristics of the output device. Similarly, when the image having the embedded code is read and input from the medium by an input device, grayscale levels of the input image differ from the grayscale levels of the original-image due to input characteristics of the input device. Due to this, values pertaining to the difference between the average densities of the adjacent block pairs in the input image differ from the corresponding values during data embedding, and the original codes cannot be decoded.
Thus, in the encoding method disclosed in Japanese Patent Laid-Open Publication No. 2004-349879, the image having the embedded code needs to be output to a medium, the output image needs to be input from the medium and decoded to determine whether the original codes can be decoded.